Synthesis, crystal structure and catalytic property of a dinuclear cobalt(III) complex derived from 2-ethyl-2-{[1-(2-hydroxy-5-methylphenyl)methylidene]amino}propane-1,3-diol

Article abstract of DOI:10.1080/24701556.2018.1503677

With a tetradentate Schiff base ligand 2-ethyl-2-{[1-(2-hydroxy-5-methylphenyl)methylidene]amino}propane-1,3-diol (H₃L) with cobalt nitrate and ammonium thiocyanate, a dinuclear cobalt(III) complex was prepared and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. The complex crystallizes in the monoclinic space group P2₁/n with unit cell dimensions a = 17.682(2) ?, b = 22.652(2) ?, c = 18.617(2) ?, β = 99.546(2)°, V = 7,353.5(12) ?³, Z = 4, R₁ = 0.0956, and wR₂ = 0.2027. Single crystal X-ray diffraction analysis reveals that the asymmetric unit of the compound contains two dinuclear cobalt(III) complex molecules, three methanol molecules and one water molecule of crystallization. The Co???Co distances in the dinuclear cobalt(III) complex molecules are about 2.97 ?. The Co atoms are in octahedral coordination. The complex has effective property on the oxidation of various aliphatic and aromatic olefins.

Full text of DOI:10.1080/24701556.2018.1503677

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt21
Synthesis, crystal structure and catalytic
property of a dinuclear cobalt(III) complex
derived from 2-ethyl-2-{[1-(2-hydroxy-5-
methylphenyl)methylidene]amino}propane-1,3-
diol
Xiao-Yang Qiu
To cite this article: Xiao-Yang Qiu (2018): Synthesis, crystal structure and catalytic
property of a dinuclear cobalt(III) complex derived from 2-ethyl-2-{[1-(2-hydroxy-5-
methylphenyl)methylidene]amino}propane-1,3-diol, Inorganic and Nano-Metal Chemistry, DOI:
10.1080/24701556.2018.1503677
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INORGANIC AND NANO-METAL CHEMISTRY
https://doi.org/10.1080/24701556.2018.1503677
Synthesis, crystal structure and catalytic property of a dinuclear cobalt(III)
complex derived from 2-ethyl-2-{[1-(2-hydroxy-5-methylphenyl)methylidene]
amino}propane-1,3-diol
Xiao-Yang Qiu
College of Science and Technology, Ningbo University, Ningbo, P. R. China
ABSTRACT
ARTICLE HISTORY
Received 9 April 2017
Accepted 16 July 2018
With a tetradentate Schiff base ligand 2-ethyl-2-{[1-(2-hydroxy-5-methylphenyl)methylidene]amino}
propane-1,3-diol (H
3
L) with cobalt nitrate and ammonium thiocyanate, a dinuclear cobalt(III)
complex was prepared and characterized by elemental analysis, IR spectroscopy and X-ray
KEYWORDS
Schiff base; cobalt complex;
crystal structure;
structure determination. The complex crystallizes in the monoclinic space group P2
1
/n with unit
ꢀ
3
cell dimensions a ¼ 17.682(2) Å, b ¼ 22.652(2) Å, c ¼ 18.617(2) Å, b ¼ 99.546(2) , V ¼ 7,353.5(12) Å ,
Z ¼ 4, R ¼ 0.0956, and wR ¼ 0.2027. Single crystal X-ray diffraction analysis reveals that the
1
2
catalytic property
asymmetric unit of the compound contains two dinuclear cobalt(III) complex molecules, three
methanol molecules and one water molecule of crystallization. The Co···Co distances in the dinuclear
cobalt(III) complex molecules are about 2.97 Å. The Co atoms are in octahedral coordination. The
complex has effective property on the oxidation of various aliphatic and aromatic olefins.
Introduction
further purification. Elemental analyses for carbon,
hydrogen, and nitrogen were carried out with an Elementar
Vario EL. Infrared spectra were measured on KBr disks with
a Hitachi I-5040 FT-IR spectrophotometer. H NMR data
were recorded on a Bruker NMR 300 MHz instrument.
In the last few decades, considerable attention has been
focused on the catalytic oxidation of olefins in the
production of chemicals and fine chemicals since epoxides
are key starting materials for a wide variety of oily
1
[
1–5]
products.
Because of the environment friendly nature,
H O has been regarded as the first selected oxidant in the Synthesis of H3L
2
2
oxidation of olefins. Transition metal complexes with
various ligands have presented interesting catalytic
5
-Methylsalicylaldehyde (1.36 g, 10 mmol) and 2-amino-2-
[6–10]
ethylpropane-1,3-diol (1.19 g, 10 mmol) were dissolved in
methanol (30 mL). The mixture was refluxed for 30 min and
the solvent was evaporated by distillation. Colorless solid
was recrysallized from methanol to give pure product of
properties.
efficient catalytic oxidation properties.
cobalt complexes are effective catalysts in the Suzuki–
Among the complexes, cobalt species show
[
11–16]
Schiff base
[
17]
Miyaura cross-coupling reactions,
the oxidation reaction
the electrocatalytic hydrogen generation
[
18]
H
3
L. Yield: 78%. Anal. Calcd. for C13
H19NO : C, 65.80; H,
3
of cyclohexane,
[
19]
[20]
8.07; N, 5.90%. Found: C, 65.67; H, 8.18; N, 5.81%. IR (KBr,
process,
as well as the hydrosilylation of olefins.
As a
ꢁ
1
ꢁ1
1
cm ) data for ꢀ(C ¼ N): 1,641 cm
.
H NMR (300 MHz,
d -DMSO): d 12.33 (s, 1H), 8.69 (s, 1H), 7.45 (s, 1H), 7.13
d, 1H), 6.93 (d, 1H), 3.77 (t, 4H), 3.51 (t, 2H), 2.32 (s, 3H),
.65 (q, 2H), 0.93 (t, 3H).
continuation of the catalytic properties of new cobalt
complexes. In this article, a new dinuclear cobalt(III)
complex (Scheme 1) with the tetradentate Schiff base ligand
6
(
1
2
-ethyl-2-{[1-(2-hydroxy-5-methylphenyl)methylidene]amino}
propane-1,3-diol (H L) was prepared and its catalytic oxida-
3
tion property was performed.
Synthesis of the complex
Equimolar quantities (1.0 mmol each) of H L (0.237 g) and
3
Experimental
cobalt nitrate hexahydrate (0.291 g) were dissolved in
methanol (20 mL). The mixture was refluxed for 30 min and
cooled to room temperature, to give a deep brown solution.
Materials and methods
5
-Methylsalicylaldehyde and 2-amino-2-ethylpropane-1,3- The solution was kept still in air for a week to slow
diol were purchased from Alfa Aesar. Cobalt nitrate and evaporate, to give brown block-shaped single crystals of the
solvents are commercially available and were used without complex. Yield: 32%. Anal. Calcd. for C H Co N O S : C,
58
88
4
6
19 2
CONTACT Xiao-Yang Qiu
xiaoyang_qiu@126.com
College of Science and Technology, Ningbo University, Ningbo 315212, P. R. China
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsrt.
ß 2018 Taylor & Francis Group, LLC

2
X.-Y. QIU
Table 1. Crystal data, data collection and structure refinement for
the complex.
Parameters
Value
N
Molecular formula
Formula weight
Crystal system
Space group
a (Å)
C
58
H
88Co
1,473.2
4
N
6
O
19
S
2
OH
Monoclinic
OH2
1
P2 /n
O
O
17.682(2)
b (Å)
22.652(2)
18.617(2)
99.546(2)
7,353.5(12)
4
Co
O
Co
N
O
c (Å)
O
ꢀ
NCS
b ( )
3
V (Å )
Z
D
ꢁ3
c
(g cm
)
1.331
F(000)
l (mm
h range ( )
3,080
1.010
2.39–25.17
ꢁ
1
)
ꢀ
hkl range
ꢁ21 ꢃ h ꢃ 20
ꢁ
26 ꢃ k ꢃ 27
Scheme 1. The cobalt complex.
ꢁ
20 ꢃ l ꢃ 22
Reflections
Collected
Unique
52,369
12,164
6,693
0.1085
818
4
5
2
7.29; H, 6.02; N, 5.70%. Found: C, 47.43; H, 5.90; N,
ꢁ
1
.61%. IR data (KBr, cm ): ꢀ(O–H), 3,451; ꢀ(NCS),
,085; ꢀ(C¼N), 1,628. UV–vis data [methanol, k/nm
Observed [I > 2r(I)]
R
int
ꢁ
1
ꢁ1
Parameters
(e/Lꢂmol ꢂcm )]: 270 (15,120), 320 (3,726), 410 (3,370),
Restraints
0
5
10 (235).
Final R index [I > 2r(I)]
R index (all data)
Goodness-of-fit on F
0.0956, 0.2027
0.1792, 0.2595
1.052
2
ꢁ
3
Maximum/minimum Dq (e Å
)
1.090, –0.735
Catalytic oxidation experiment
Catalytic experiment was carried out in a 50 mL glass
round-bottom flask fitted with a reflux condenser and Table 2. Selected bond distances (Å) and angles ( ) for the complex.
ꢀ
placed in an oil bath at prearranged temperature under Co(1)–O(1)
1.890(5)
1.894(5)
1.908(6)
2.030(5)
2.050(10)
2.117(9)
1.891(5)
1.900(6)
1.913(5)
2.018(5)
2.073(6)
2.125(5)
94.1(2)
88.0(2)
90.0(2)
85.4(2)
92.6(2)
89.5(2)
91.3(2)
85.5(3)
98.7(3)
92.7(2)
89.1(3)
93.7(3)
92.0(3)
90.7(2)
178.5(3)
89.9(2)
90.1(3)
94.9(2)
92.2(2)
90.3(2)
177.2(2)
83.9(2)
86.5(2)
93.2(2)
79.67(19)
171.9(2)
89.5(3)
89.5(2)
92.3(3)
91.1(2)
Co(1)–O(2)
Co(1)–O(5)
Co(1)–N(2)
Co(2)–O(5)
Co(2)–O(6)
Co(2)–O(3)
Co(3)–O(8)
Co(3)–N(4)
Co(3)–O(12)
Co(4)–N(6)
Co(4)–O(12)
Co(4)–O(10)
1.897(5)
1.887(5)
1.894(6)
2.043(5)
2.100(6)
2.126(6)
1.898(5)
1.911(6)
1.914(5)
2.042(8)
2.074(5)
2.134(5)
177.7(2)
84.6(2)
94.4(2)
179.4(2)
90.0(2)
94.4(3)
172.9(3)
78.1(2)
176.1(3)
88.9(2)
170.4(3)
89.7(4)
88.5(2)
91.4(3)
86.6(3)
93.6(3)
89.3(3)
174.2(3)
177.8(2)
84.6(2)
91.4(2)
93.0(2)
175.2(3)
91.6(3)
95.6(3)
91.0(2)
86.8(2)
87.2(2)
92.3(2)
178.0(2)
Co(1)–O(4)
continuous stirring. The oxidation was carried out as
follows: the complex (0.032 mmol) was dissolved in 10 mL
Co(1)–N(1)
Co(2)–O(2)
1
,2-dichloroethane. Then 10 mmol alkene was added to the Co(2)–N(3)
Co(2)–O(7)
reaction mixture and 30 mmol TBHP was added. The
reaction mixture was refluxed for 1 h. The reaction products
Co(3)–O(11)
Co(3)–N(5)
were monitored at periodic time intervals using gas Co(3)–O(9)
Co(4)–O(9)
Co(4)–O(14)
Co(4)–O(13)
chromatography. The oxidation products were identified by
comparison with authentic samples (retention times in GC).
O(5)–Co(1)–O(1)
O(5)–Co(1)–O(4)
O(5)–Co(1)–N(2)
O(4)–Co(1)–N(2)
O(1)–Co(1)–O(2)
N(2)–Co(1)–O(2)
O(1)–Co(1)–N(1)
N(2)–Co(1)–N(1)
O(2)–Co(2)–O(5)
O(5)–Co(2)–N(3)
O(5)–Co(2)–O(6)
O(2)–Co(2)–O(7)
N(3)–Co(2)–O(7)
O(2)–Co(2)–O(3)
N(3)–Co(2)–O(3)
O(7)–Co(2)–O(3)
O(11)–Co(3)–N(5)
O(11)–Co(3)–N(4)
N(5)–Co(3)–N(4)
O(8)–Co(3)–O(9)
N(4)–Co(3)–O(9)
O(8)–Co(3)–O(12)
N(4)–Co(3)–O(12)
O(9)–Co(4)–N(6)
N(6)–Co(4)–O(14)
N(6)–Co(4)–O(12)
O(9)–Co(4)–O(13)
O(14)–Co(4)–O(13)
O(9)–Co(4)–O(10)
O(14)–Co(4)–O(10)
O(13)–Co(4)–O(10)
O(1)–Co(1)–O(4)
O(1)–Co(1)–N(2)
O(5)–Co(1)–O(2)
O(4)–Co(1)–O(2)
O(5)–Co(1)–N(1)
O(4)–Co(1)–N(1)
X-ray structure determination
Data collection for the complex was performed with a
Bruker Apex II CCD diffractometer at 298 K. The structure
was solved by direct methods with SHELXS-97 and refined O(2)–Co(1)–N(1)
2
[21]
O(2)–Co(2)–N(3)
O(2)–Co(2)–O(6)
N(3)–Co(2)–O(6)
by full-matrix least squares (SHELXL-97) on F .
All
non-hydrogens were refined anisotropically. Hydrogens
were placed geometrically and refined with a riding model, O(5)–Co(2)–O(7)
O(6)–Co(2)–O(7)
O(5)–Co(2)–O(3)
O(6)–Co(2)–O(3)
with isotropic displacement coefficients U(H)¼1.2 U(C) or
1
.5 U(C
and O). Crystallographic data for the complex
methyl
are summarized in Table 1. Selected bond lengths and angles O(11)–Co(3)–O(8)
O(8)–Co(3)–N(5)
are listed in Table 2.
O(8)–Co(3)–N(4)
O(11)–Co(3)–O(9)
N(5)–Co(3)–O(9)
O(11)–Co(3)–O(12)
N(5)–Co(3)–O(12)
O(9)–Co(3)–O(12)
O(9)–Co(4)–O(14)
Results and discussion
Synthesis and general characterization
The Schiff base ligand was prepared by the reaction of O(9)–Co(4)–O(12)
O(14)–Co(4)–O(12)
N(6)–Co(4)–O(13)
O(12)–Co(4)–O(13)
equimolar quantities of 5-methylsalicylaldehyde and
2
-amino-2-ethylpropane-1,3-diol in methanol, followed by
recrystallization from methanol. The cobalt complex was N(6)–Co(4)–O(10)
O(12)–Co(4)–O(10)
prepared by the reaction of equimolar quantities of the

INORGANIC AND NANO-METAL CHEMISTRY
3
ꢀ
Schiff base ligand with cobalt nitrate and ammonium Table 3. Hydrogen bond distances (Å) and bond angles ( ) for the complex.
thiocyanate in methanol, followed by slow evaporation. The D–HꢂꢂꢂA
d(D–H)
d(HꢂꢂꢂA)
d(DꢂꢂꢂA)
Angle (D–HꢂꢂꢂA)
oxidation state of the Co atom in the complex was oxidized O(19)–H(19)ꢂꢂꢂN(3)
0.82
0.82
0.82
0.82
0.82 Å
0.82
0.85
0.85
0.85
0.93
0.93
2.63
2.47
2.09
2.62
2.08
2.01
1.96
2.02
2.00
1.80
1.87
3.45(1)
3.17(1)
2.69(1)
3.41(1)
2.68(1)
2.80(1)
2.60(1)
2.76(1)
2.65(1)
2.65(1)
2.61(1)
174
144
130
162
130
160
131
145
132
152
135
i
O(18)–H(18)ꢂꢂꢂO(8)
to þ3 by air. Crystals of the complex are stable in air, and
i
O(18)–H(18)ꢂꢂꢂO(11)
ii
ii
soluble in methanol, ethanol, DMF and DMSO, insoluble in O(17)–H(17A)ꢂꢂꢂO(1)
O(17)–H(17A)ꢂꢂꢂO(4)
water. The Schiff base ligand and the cobalt complex
have been characterized by elemental analyses and infrared
ii
O(16)–H(16)ꢂꢂꢂO(1)
iii
O(15)–H(15B)ꢂꢂꢂO(6)
spectroscopy. In the spectrum of the Schiff base, the typical O(15)–H(15A)ꢂꢂꢂO(12)
iii
O(14)–H(14A)ꢂꢂꢂO(16)
band indicative of the C¼N bond was observed at
iii
O(10)–H(10C)ꢂꢂꢂO(19)
ꢁ
1
1
,641 cm . In the spectrum of the complex, the broad and
iv
O(3)–H(3A)ꢂꢂꢂO(18)
medium band indicative of the O–H vibrations was centered
Symmetry codes: (i) 1 – x, –y, –z; (ii) –x, –1 – y, –z; (iii) 1 þ x, y, z; (iv) –1 þ x,
y, z.
ꢁ
1
ꢁ1
at 3,451 cm . The strong band at 2,085 cm
attributed to the vibration of the thiocyanate ligand. The
intense and typical absorption for the C¼N bond was complex molecules are about 2.97 Å. The Co(1) and Co(3)
can be
ꢁ
1 [22]
located at 1,628 cm
,
which shifted to lower frequency atoms are coordinated by two phenolate O, two imine N
when compared to the free Schiff base.
and two bridging hydroxyl O atoms from two Schiff base
ligands, forming octahedral coordination. The Co(2) and
Co(4) atoms are coordinated by two bridging hydroxyl O
atoms, two terminal hydroxyl O atoms, one thiocyanate N
Crystal structure description of the complex
The asymmetric unit of the compound contains two atom, and one water O atom, forming octahedral coor-
dinuclear cobalt(III) complex molecules (Figures 1 and 2), dination. The distortion of the octahedral coordination
four methanol molecules and one water molecule of crystal- can be observed from the cis and trans coordinate bond
ꢀ
ꢀ
lization. The Co···Co distances in the dinuclear cobalt(III) angles, viz. 84.6(2)–94.4(3) and 172.9(3)–179.4(2) for
Figure 1. The molecular structure of the Co(1) and Co(2) complex molecule with 30% probability thermal ellipsoids.
Figure 2. The molecular structure of the Co(3) and Co(4) complex molecule with 30% probability thermal ellipsoids.

4
X.-Y. QIU
and aromatic substrates. In general, oxidation of aromatic
substrates gave the corresponding epoxides in over 80%
yields, while in the oxidation of aliphatic substrates, the
conversion is lower than 70%. This might be caused by the
isolated double bonds are less reactive than the conjugated
ones. For both aliphatic and aromatic substrates, the con-
version for the chloro-substituted species is higher than the
methyl or no substituted ones. It can be concluded that
the electronic-withdrawing effect of the chloro group is
more active than the electronic-donating effect of the methyl
group, and also more active than the compounds with no
substituted groups.
Supporting information
CCDC-1448087 contains the supplementary crystallographic
data for this paper. These data can be obtained free of
charge at http://www.ccdc.cam.ac.uk/const/retrieving.html or
from the Cambridge Crystallographic Data Centre (CCDC),
1
3
2 Union Road, Cambridge CB2 1EZ, UK; fax: þ44(0)1223-
36033 or e-mail: deposit@ccdc.cam.ac.uk.
Figure 3. Molecular packing structure of the complex, viewed along the c axis.
Hydrogen bonds are shown as dashed lines.
Funding
This work was financially supported by K.C. Wong Magna Fund
in Ningbo University, Ningbo natural science fund (Project No.
Table 4. Catalytic oxidation results.
a
Substrate
Product
Conversion (%)
53
201701HJ-B01019), Ningbo education research project (Project
O
No. 2017YZD001) and planning project of philosophy and social
science in Zhejiang province (Project No. 17NDJC128YB).
68
Cl
Cl
O
O
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